perf(scene): per-entity tessellation memo for the render path

Phase 2.2. wires_for_block_culled re-tessellated every visible entity on
any geometry bump, so a single-entity edit cost a full model re-tess
(~30ms baseline after the block_epoch fix).

Add a per-entity memo (tess_memo: Handle -> Arc<Vec<WireModel>>) on the
culled Model render path. It's guarded by a hash of the tessellation
parameters (tol / view / anno / world_offset / bg / entered viewport); a
mismatch (zoom, layout switch) clears it. The render path now classifies
the visible set against the memo, materializes hits and tessellates only
the misses in parallel, then stores the misses back.

- bump_geometry clears the memo (structural change — safe default);
- incremental edits drop just the changed handle via mark_entity_dirty
  and bump with bump_geometry_no_blocks: line commit (new handle is a
  natural miss) and grip commit / Esc-cancel (mark the dragged handle).

The hit-test (view_aabb == None), paper and per-viewport paths bypass the
memo so their differing cull parameters don't thrash it. A single-entity
edit now skips the per-entity geometry math for the entire unchanged set;
the Vec assembly + batched-buffer upload stay O(N).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

ROADMAP.md

@@ -119,7 +119,23 @@ read-only over the finished `defns` map and re-walks shared nested defns
 (no memo), so the per-name resolves fan out across rayon (read phase), then a
 serial phase stores each AABB back.
 
-### 2.2 Incremental wire cache (delta tessellation)
+### 2.2 Incremental wire cache (delta tessellation) ✅ DONE (render path)
+
+A per-entity tessellation memo (`tess_memo`, `Handle → Arc<Vec<WireModel>>`)
+sits inside `wires_for_block_culled` on the culled Model render path. It's
+keyed by a guard hash of the tessellation parameters (tol / view / anno /
+offset / bg / entered viewport); a mismatch (zoom, layout) clears it.
+`bump_geometry` clears it (structural change); incremental edits drop just the
+changed handle via `mark_entity_dirty` and bump with `bump_geometry_no_blocks`.
+So a single-entity edit (line commit, grip commit/cancel) re-tessellates only
+that entity and reuses every other — the per-entity geometry math is skipped
+for the unchanged set. The hit-test (`view_aabb == None`), paper and
+per-viewport paths bypass the memo so their cull params don't thrash it.
+
+Remaining: the assembly still concatenates into one `Vec` and rebuilds the
+batched GPU buffer (O(N) clone + upload), and the uncalled hit-test
+(`entity_wires_arc`) still rebuilds on edit — driving those to true O(1)
+needs per-handle GPU slots, which trade against the single-draw batch (3.3).
 
 `bump_geometry()` invalidates the whole wire cache today
 ([`scene/mod.rs:650`](src/scene/mod.rs#L650)). Edits usually touch 1-2